麦克斯韦方程中有某些特性是恒定不变的——磁场强度、电位移场以及描述电磁场电通量的坡印廷矢量。
Maxwell's equations conserve certain properties-the magnetic field intensity, the electric displacement field and the Poynting vector that describes the electric flux of an electromagnetic field.
如果取的向量场是处处恒定的，所有点都是平移关系，所以没有散度，因为导数为零。
If you take a vector field that is a constant vector field where everything just translates then there is no divergence involved because the derivatives will be zero.
假设晶体侧面保持恒定的温度，讨论了不同泵浦源下，激光晶体的三维温度场的分布。
With different pump source, the three-dimensional temperature field in the laser crystal was simulated on condition that the temperature on the crystal side remained constant.
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